The present invention relates, in general, to methods for sanitizing food processing equipment and food contact surfaces and, more particularly, to food processing sanitization methods using ozone.
Microbial outgrowth is a major cause of food spoilage. The presence of pathogenic microorganisms on food products can potentially lead to food-borne outbreaks of disease and cause significant economic loss to food processors. The need to delay the onset of spoilage has led the food processing industry to seek effective means for disinfecting food products in order to ensure food safety. Currently, food processors use several different technologies to eliminate, retard or prevent microbial outgrowth. For example, techniques such as heating, radiation and application of chemical agents are currently in use.
Microbial contamination of food products can occur not only from the product itself, but also from the environment. For example, food products are susceptible to microbial contamination during processing steps carried out after the initial sanitization process. Contamination sources from the food processing environment can include processing equipment, such as knives and mixers, food contact surfaces, such as cutting boards, conveyor belts and interior surfaces, such as floors, walls and ceilings. An additional source of contamination in the food processing environment can also be the ambient air within a food processing facility.
Current methods for sanitizing food processing areas include the use of heat or chemicals to clean floors, walls and food contact surfaces. While the use of steam or hot water can be effective, its efficiency is low on large surface areas. In addition to water, chemical sanitizers, such as chlorine and quaternary ammonium compounds are also in use. Although chemical sanitizers can be effective, there efficacy can vary with respect to different microorganisms present in a food processing environment. Additionally, chemical sanitizers are themselves toxic and they can alter the taste the food that comes in contact with a chemically sanitized surface. Further, the use of chemical sanitizers requires that the chemicals be stored near their point of use and they have safety problems associated with their storage, handling and transportation.
Ozone sanitization methods have proven to be highly effective when applied directly to food products. Ozone has been shown to be a highly reactive oxidant that is capable of destroying most cellular constituents of pathogenic microorganisms. Additionally, ozone advantageously naturally decomposes into oxygen. At low levels, ozone will decompose into oxygen within a few hours. Ozone is normally produced by irradiating an oxygen-containing gas with ultraviolet light or by corona discharge. Ozone processes have been developed using an ozone solution made by injecting ozone gas into water that is used to sanitize and disinfect food products.
While the use of ozone has proven effective at controlling microbial outgrowth on food products, the generation and use of ozone must be carefully controlled to prevent injury to food processing personnel. For example, high concentrations of ozone can be toxic to humans. The Occupational Safety and Health Administration (OSHA) specifies that ozone exposure in the workplace should not exceed 0.1 parts-per-million (ppm) for an eight hour workshift or 0.3 ppm for fifteen minutes and not to be repeated more than twice during an eight hour workshift. In order to meet OSHA requirements, ozone generation and handling systems used in the food processing industry must be properly vented to ensure that workers are not overexposed to ozone. Collecting and containing ozone gas requires expensive, carefully regulated equipment that adds significantly to the cost of food processing operations. In addition to equipment costs, the excess ozone gas must be vented, which represents a loss of an expensive process gas. While ozone sanitization methods have proven effective, improved methods of utilizing ozone for sanitizing a food processing environment are still needed.
The present invention provides a method of sanitizing a food processing environment. In one aspect, the method includes preparing an aqueous ozone wash solution for use in sanitizing food contact surfaces and food processing workspaces. The method further provides for collecting ozone off-gas from the aqueous ozone solution. The collected ozone off-gas is then introduced into an ambient of the food processing environment. The method of the invention further includes sanitizing the food processing workspace, food storage containers and food processing equipment using the collected ozone off-gas.
In another aspect of the invention, ozone gas is directly generated and discharged into a food processing workspace. Where either directly generated ozone gas or ozone off-gas is introduced into the ambient of the food processing workspace, the ozone concentration is maintained within exposure limits specified by OSHA. For example, the ozone concentration level is maintained at about 0.05 ppm or less. Thorough circulation of ozone within the workspace ambient is provided by air distribution systems within the workspace.
In a further aspect of the invention, an ozone off-gas stream is generated to provide a constant product Cxc2x7T where C is the ozone dose mg/min and T is the surface contact time in minutes. The ozone off-gas stream is produced at an ozone flow rate of about 0.1 to about 15 liters per second.
In a still further aspect of the invention, the ozone off-gas is mixed with a feed gas prior to introducing the ozone off-gas into an ambient of the food processing environment. The feed gas can be oxygen, air, a mixture of oxygen and air, a mixture of the oxygen, air and an inert gas. The inert gas can include argon, krypton, xenon, neon, carbon dioxide (CO2) and nitrogen.
The invention further includes preparation of an ozone wash solution from which the off-gas is collected. The ozone solution can have an ozone concentration ranging from about 0.1 ppm to about 15 wt %.
The present invention further contemplates the use of the collected ozone off-gas or an ozone wash solution or both to disinfect food contact surfaces, interior surfaces of food processing facilities, and food processing equipment. The ozone wash solution can be prepared as a continuous stream of ozone wash solution or in batches of solution. In either method, ozone off-gas is continuously collected for use in sanitizing the food processing environment.
In the present invention, ozone gas is produced by either bombarding oxygen with ultraviolet radiation at a wavelength below about 200 nm or through the use of a corona discharge. Alternatively, an oxygen-containing gas, such as air and the like, can be used to generate ozone. The ozone generator is configured such that the generated ozone gas can be sparged into an aqueous solution for the production of an ozone wash solution.
The ozone produced by the ozone generator can be mixed with a feed gas prior to sparging the ozone into the aqueous solution. The feed gases include oxygen, air, a mixture of oxygen and air, an inert gas, a mixture of air, oxygen and the inert gas, and the like. The inert gases can be nitrogen, carbon dioxide, argon, krypton, xenon, neon and mixtures thereof. In an alternative method, the feed gas is sparged into the aqueous solution separately, rather than being mixed with ozone prior to sparging.
Preferably, the ozone sparging process is carried out in a tank into which an aqueous solution is supplied. In one embodiment, the aqueous solution is primarily water. However, the water can contain chemical agents, such as small quantities of chlorine added to city water, and the like. In a preferred process, the inert gas makes up about 10 to about 99 weight percent of the total gas sparged into the aqueous solution. The sparging process can be carried out over a wide temperature range in which the aqueous solution is maintained at a temperature below about 70xc2x0 C. Ozone solution is withdrawn from the sparging apparatus having a concentration of about 0.1 ppm to about 15 wt %. In one embodiment, a continuous aqueous ozone stream is withdrawn from the sparging apparatus at a flow rate ranging from about 0.1 liters per second to about 15 liters per second. In an alternative embodiment, aqueous ozone solution is prepared in a batch system. In the batch system, many gallons of aqueous ozone solution are prepared and then transferred to ozone distribution systems within the food processing facility.
With either the continuous stream or the batch aqueous ozone method, the ozone solution is delivered throughout the food processing facility through a distribution system, such as piping systems and the like. At the various point-of-use locations, the ozone can be applied to interior surfaces, food contact surfaces and process equipment by means of spray nozzles, misting devices and the like.
In accordance with the invention, a vapor collection device is provided within the ozone sparging apparatus to collect ozone vapor as an off-gas from the aqueous solution. In the preparation of an aqueous ozone solution, considerable ozone can be lost because of the relative solubility of ozone. The off-gassing of ozone from the aqueous solution represents an ozone loss mechanism in the aqueous ozone preparation process. In accordance with the invention, the existing ozone loss mechanism is advantageously employed to provide a source of gaseous ozone for sanitizing a food processing environment.
In one embodiment of the invention, the collected ozone off-gas is used to produce a continuous gaseous ozone stream that is subsequently distributed to points-of-use throughout a food processing environment. The gaseous ozone stream is provided at a flow rate varying from about 0.1 liters per second to about 15 liters per second. For application of the ozone off-gas to processing equipment and food contact surfaces, the ozone concentration can vary from about 0.1 ppm to about 15 wt %. Correspondingly, where the ozone off-gas stream is to be introduced into the air within a workspace, the ozone concentration is regulated to within OSHA standards. To ensure worker safety, the ozone concentration is regulated in conjunction with the air distribution systems within the workplace to ensure that the ozone concentration within the workspace does not exceed a safe level. For example, current OSHA standards require that the ozone level not exceed 0.1 ppm for an eight hour workshift. This limit can be met by, for example, limiting the ozone concentration to a range of preferably no more than about 0.10 ppm and more preferably about 0.02 ppm to about 0.05 ppm. The ozone off-gas can be diluted to within a desired concentration range by mixing the ozone off-gas with a feed gas. In a present embodiment, any of the previously described feed gases can be mixed with the ozone off-gas prior to introduction into a workspace.
Where the ozone off-gas is to be introduced into a food storage ambient, such as food storage container, and the like, the ozone concentration can exceed workspace limits. For example, the ozone concentration can be similar to that used to sanitize food contact surfaces and processing equipment.